This Heathkit IG-4505 Oscilloscope Calibrator has an accurate, crystal controlled, 50 ohm, fast rise square wave generator. It also provides hi Z dc levels from 1 mv to 100 vdc. It can also serve as a bench standard to calibrate other equipment. This unit is in excellent condition and works well. Included is the original manual. Please contact me for additional pictures and technical details. $45 plus shipping.